The invention is based on a priority application EP04291664.3 which is hereby incorporated by reference.
The present invention relates to a method for transmitting data between a mobile client and a cellular network, wherein the mobile client is connected to an ad-hoc network and communicates via the ad-hoc network with a mobile relay that is connected to the ad-hoc network and the cellular network and wherein the mobile relay relays data that are transmitted from the mobile client to the cellular network and/or data that are transmitted from the cellular network to the mobile client.
The invention also relates to a mobile relay for relaying data that are transmitted from a mobile client to a cellular network and/or for relaying data that are transmitted from a cellular network to a mobile client wherein the mobile client is connected to the ad-hoc network and the mobile relay is connected to the ad-hoc network and to the cellular network.
The invention furthermore relates to a mobile client connected to an ad-hoc network and to a radio access network that is part of a cellular network and adapted to transmit signaling, data dedicated to a mobile relay, and data dedicated to a mobile client, wherein the radio access network comprises a radio access network protocol stack and wherein the radio access network protocol stack comprises a set of lower layers and a set of higher layers.
The invention at least relates to a telecommunications system comprising a cellular network, an ad-hoc network, a mobile client and a mobile relay wherein the mobile client is connected to an ad-hoc network and comprises means for communicating with the mobile relay via the ad-hoc network, and wherein the mobile relay is connected to the ad-hoc network and the cellular network and comprises means to relay data that are transmitted from the mobile client to the cellular network and/or data that are transmitted from the cellular network to the mobile client.
Cellular networks are widely used for enabling communication between a mobile terminal and another mobile terminal or between a mobile terminal and a terminal that is connected to a terrestrial network, e.g. the public switched telephone network (PSTN), the integrated services data network (ISDN) or the internet. It is also possible for a mobile terminal to access different services offered directly by a cellular network operator to its subscribers (e.g. the mobile terminals), based on different service platforms located in the Core Network.
A cellular network consists of different network elements such as a Core Network (CN), a Radio Access Network (RAN), and a mobile terminal (also called User Equipment, UE) e.g. a mobile telephone. Examples of cellular networks are GSM (Global System for Mobile communications) and UMTS (Universal Mobile Telecommunications System). In the remaining text the terminology according to the UMTS standard is used.
The Radio Access Network (RAN) is composed of a collection of Radio Network Subsystems (RNS). Each RNS includes a Radio Network Controller (RNC) and several Node Bs that are attached to and controlled by the RNC.
The Node B is a physical unit for radio transmission (and reception) and is attached to one or more cells. The main task of the Node B is the conversion of data transmitted to and from the mobile terminal. In addition, the Node B measures the quality and strength of the connection to the mobile terminal.
The RNC is responsible for the control of its associated Node Bs. Thus, it is in charge of the management of resources in those Node Bs and in the cells to which these Node Bs are attached.
The different elements of the RAN are interconnected with each other and towards the Core Network by means of a transmission network, which is usually a terrestrial network. Consequently, the RAN is named UTRAN (UMTS Terrestrial Radio Access Network). In UTRAN, the transmission network can be based on ATM or IP transport. Initial releases of the UMTS standard were only allowed for the use of ATM, but IP transport was introduced as an option in Release 5.
Several logical interfaces have been defined for the interconnection of different types of network elements across the transmission network. In particular, the communication between an RNC and any of the Node Bs belonging to the same RNS takes place across the so-called Iub interface. Moreover, different RNCs (belonging to different RNSs) may communicate with each other using the so-called Iur interface. Finally, the communication between an RNC and the Core Network (and hence between RAN and CN) takes place across a so-called Iu interface.
In UTRAN, the RNC may play several roles with respect to the different Node Bs and terminals. In each RNS, there is a single RNC, which is responsible for the control of all Node Bs in the RNS and their associated resources. In this case, the RNC acts as a Controlling RNC (CRNC) for the Node Bs in the RNS. In addition to the control of Node Bs, the RNC is also responsible for controlling the connection of the mobile terminals to the cellular network. The RNC in charge of a particular user connection acts as a Serving RNC (SRNC) for the user.
A mobile terminal accesses the cellular network via one or several radio links which are accessible through a so called air interface. Data transmitted from the mobile terminal are carried over the air interface to one or several Node Bs. Each Node B transmits the data received from the mobile terminal together with measurement results to the associated Controlling RNC, via the Iub interface.
The Controlling RNC for a Node B through which the mobile terminal is accessing the network may also be the Serving RNC for the mobile terminal or a different RNC. In the latter case, the Controlling RNC for the Node B plays also the role of a Drift RNC with respect to the user connection, because data must be forwarded (“drifted”) via the Iur interface by this RNC to the Serving RNC responsible for the control of the user connection.
In UMTS the Core Network consists of a circuit-switched part (CS domain) and a packet-switched part (PS domain). Each of them is composed of several elements. One major element in the CS domain is the Mobile Switching Center (MSC), responsible e.g. for switching and signaling functions for mobile terminals, including support of user mobility through handover and location update procedures. Moreover, access to external circuit-switched networks may be provided through a so called Gateway MSC. The MSC communicates with a Home Location Register (HLR) and a Visitor Location Register (VLR) which are databases storing permanent subscriber information and temporary user location information, respectively.
In the PS domain, a Serving GPRS Support Node (SGSN) can be considered as the counterpart of the MSC. The SGSN is responsible for managing the packet-switched related communications within the CN. The SGSN communicates with a Gateway GPRS Support Node (GGSN), which provides access to an external packet-switched network such as the Internet. A network address is assigned to each mobile terminal by the GGSN. This network address is valid in the external packet-switched network. This allows the mobile terminal to communicate with other terminals or servers in the external network.
Data that originate from the mobile terminal are transmitted through the Core Network (CN) to the receiver. This is for example a terminal connected to an external circuit-switched network such as the ISDN, an external packet-switched network like the Internet or another mobile terminal. If the receiver is another mobile terminal the data are transmitted from the CN to this mobile terminal via its associated Serving RNC and the Node B that controls the cell in which the other mobile terminal is located or the Node Bs responsible for those cells in which the terminal has an active radio link, in case of soft handover (described later in this document).
The transmission of data described so far relates mainly to user data, e.g. voice related data, that are dedicated to a specific receiver. Besides this user data, within a cellular network several control information have to be transmitted to make sure the cellular network operates properly. This control information is called signaling. Signaling related data deal with subjects like handover control (including macro diversity), power control, exchange of measurements between network and terminals, mobility and location management.
A mobile terminal can be connected to several cells simultaneously. This option is called macro diversity. The set of cells the mobile terminal is connected to simultaneously is called the active set of the mobile terminal. The data streams received via the different cells of the active set are combined by the Node B (in case of softer handover, i.e. several cells in the active set belong to the same Node B) or by the RNC (in case of soft handover, i.e. cells in the active set belong to different Node Bs). The mobile terminal measures the signal levels of these cells and reports the measurement results via the controlling Node Bs to the RNC. The RNC evaluates the reported data and causes the mobile terminal to change the set of active cells if necessary.
Soft handover involves the addition of a new radio link through another Node B in case of transmission quality deterioration to improve transmission quality (e.g. by reducing the error frame rates) and to improve the rate of high quality active connections in one cell.
Since the same frequencies are used in an active cell and in the adjacent cells, there exists the risk of interference. Thus, power control is an important issue. Different power control techniques exist in UMTS, e.g. open-loop power control and closed loop power control. According to open loop power control, the Node B broadcasts information about the minimum power needed to enable a mobile terminal to gain access to the cellular network. According to the closed loop power control, the Node B transmits information to the mobile terminal to adjust the transmission power, according e.g. to a signal-to-interference ratio. The closed loop power control is a kind of dedicated signaling, since those information are not sent to all mobile terminals that reside in a cell (via broadcasting) but is dedicated to one specific mobile terminal.
The UMTS radio interface protocol stack comprises a physical layer, several L2 (layer 2) protocols, and different L3 (layer 3) protocols used for the exchange of signaling between the cellular network and the terminals. From the lowest to the highest layer, L2 protocols include the following layers: MAC (Medium Access Control), RLC (Radio Link Control), BMC (Broadcast/Multicast Control, used only for Cell Broadcast Services) and PDCP (Packet Data Convergence Protocol, used only for packet-switched services).
Some of the L3 protocols used for signaling exchange are terminated in the Core Network, and only the RRC (Radio Resource Control) protocol is terminated in the RAN. The RRC protocol is responsible for all signaling related to the usage of a radio interface to gain access to the cellular network.
Data transferred within UMTS can be divided into two groups. These are represented by control channels for transmitting signaling related data and traffic channels for transmitting user data. Examples for control channels and traffic channels are                the Broadcast Control Channel (BCCH): Broadcast of system information, i.e. information related to the radio environment like code values in the cell and in the adjacent cells, power levels, etc.        the Paging Control Channel (PCH): Paging is performed in order to find out the actual location of the user and to notify the user of the arrival of an incoming call.        the Common Control Channel (CCCH): Used for tasks common for all mobile terminals residing in the cell, for instance the initial access procedures. Since many users may use the CCCH simultaneously they are identified by unique identity (IMSI, International Mobile Subscriber Identifier, or U-RNTI, UTRAN Radio Network Temporary Identity).        the Dedicated Control Channel (DCCH): Control information of dedicated and active connection, used for instance for handover control and measurement exchange.        Dedicated Traffic Channel (DTCH): Channel for the transmission of dedicated user traffic (user data), e.g. voice data.        Common Traffic Channel (CTCH): Information that is to be send to all mobile terminals or a specific group of mobile terminals in the cell. This channel is mainly used for Cell Broadcast Services, which consist in the delivery of short text messages to all users or to the subscribed users in a cell (e.g. for short news services).        
The channels described so far are called logical channels, which can be considered as transmission services offered by the MAC layer to higher sublayers.
Logical channels are mapped to transport channels by the MAC sublayer, which may also multiplex several logical channels into the same transport channel. Transport channels are bearer services (i.e. transmission services) offered by the physical layer of the air interface.
The physical layer maps transport channels to physical channels. Physical channels correspond to the actual radio channels used for the communication across the radio interface. In addition to mapping transport channels to physical channels, the physical layer can also multiplex several transport channels onto a Coded Composite Transport Channel (CCTrCH), which is then mapped to one physical channel or more than one physical channel (in case the maximum data rate which can be offered by a single physical channel is lower than the joint data rate of the CCTrCH).
For extending a cellular network an ad-hoc network can be used. With an ad-hoc network extension a mobile terminal (here: mobile client) that is connected to the ad-hoc network communicates with the cellular network not directly but via another mobile terminal (here: mobile relay). The mobile relay is connected to the ad-hoc network and to the cellular network. Data that are transmitted from the mobile client and are dedicated to the cellular network are first transmitted from the mobile client to the mobile relay using the ad-hoc network. The mobile relay then relays these data by forwarding it to the cellular network. Examples of an ad-hoc network are WLAN (wireless local area network) and Bluetooth.
Extending a cellular network by an ad-hoc network can result in an improvement of cell capacity and coverage. If, for example, a mobile terminal is placed far away (in terms of reception level, and not necessarily physical distance) from a Node B that is in the active set of the mobile terminal, it transmits data with a very high transmission power. This in turn can interfere with other data transmissions in the same or adjacent cells. Using an ad-hoc network extension and having a mobile relay within reach of the mobile terminal, the mobile relay can connect to a Node B with a higher quality and lower power transmission than the mobile terminal. Thus the coverage can be raised and the risk of interference with other connections will be reduced. Since one mobile relay can in principle relay the data transmitted from different mobile terminals at a given time, the coverage can be increased further on.
The communication between the mobile relay and the mobile client can also be realized across a number of intermediate so called ad-hoc terminals such that the data that are transmitted from the mobile terminal and that are dedicated to the cellular network (or vice versa) are forwarded several times by intermediate ad-hoc terminals between the mobile client and the mobile relay. This is called a multi-hop ad-hoc connection.
Transmitting data between a mobile client and a cellular network via an ad-hoc extension induces an overhead since it requires several steps of processing and/or converting these data. This usually is a computing-time consuming task which is at least at the expense of computing power in one of the elements involved in the transmission of data.
For each communication connection via the ad-hoc network at least two mobile terminals are involved, namely the mobile client which communicates indirectly with the cellular network and a mobile relay that communicates directly with the cellular network. This means, that at least control data for both—the mobile relay that communicates directly with the cellular network and the mobile client—have to be transferred via the cellular network. This induces a further overhead since for just one communication connection at least two sets of control data have to be generated, transferred via the cellular network, and processed.